Denbighshire County Council is urging dog owners to clean-up after their pets after a child playing rugby on Cae Ddol fields in Ruthin got dog mess on her gum guard.
The council said the incident could have had "serious consequences for the girl's health".
Councillor David Smith, Cabinet Lead Member for Environment, said: “ I am disgusted and disappointed by this lack of concern by certain dog owners disregarding all the messages regarding the consequences of dog fouling on the health of our children.
“The Council has been running a campaign, educating and encouraging people to clean up after their animals. The majority of people do act responsibly and carry bags with them.
“However, there are some individuals who think it’s appropriate not to clear the mess."
The council says in the Ruthin incident, the child did not suffer any reactions or lasting effects but it still would have been "a very unpleasant experience for her and her family and the consequences could have been serious."